Field devices, such as radar level gauges, are suitably used for measuring the level of products such as process fluids, granular compounds and other materials. An example of such a radar level gauge can include a microwave unit for transmitting microwaves towards the surface and receiving microwaves reflected by the surface, processing circuitry arranged to communicate with the microwave unit and to determine the level based on a relation between transmitted and received microwaves.
In recent years, there has been an increasing demand for wireless measurement devices or systems with other limitations on power consumption, such as for example so called loop-powered systems that are connected by a 4-20 mA current loop. Wireless measurement devices may for example be powered by batteries or solar power. For such devices it is advantageous to improve the energy efficiency e.g. in order to increase the lifetime of batteries. Therefore, novel measurement devices having improved power efficiency are required in order to improve on conventional radar level gauges.
One approach leading to reduced power consumption is to reduce the time of the measurement, i.e. to make the measurement faster. However a shorter measuring time in combination with a continuous measurement scheme commonly used in radar level gauges will provide a large number of measurement results. An abundance of results may not necessarily lead to an improvement in either measurement accuracy or reliability. Furthermore, it is also increasingly difficult to handle and store the increasing amount of data generated, in particular given a limitation on energy consumption. Therefore, intermittent operation of a radar level gauge system where the system only performs a measurement at given time-intervals is an attractive alternative in order to improve energy efficiency.
However, there are problems associated also with intermittent measurements. For example, the system may be configured to wake up and perform a measurement at regular intervals and if the surface properties of the product to be measured are varying over time, a measurement may provide an unreliable result. Furthermore, the next measurement may also be unreliable, and so on, which may lead to long time periods between reliable measurements and unstable level readings.
Accordingly, there is a need for an improved level gauge system and a method for intermittently measuring the filling level of a product in a tank.